While there are of course many differences between Cain’s and Gingrich’s purported affairs—one important one certainly being that Gingrich’s is old news whereas Cain’s was a more recent development—recently published research in the journal Political Behavior suggests another possible factor: the race of the candidates. In the previous US presidential election cycle, Adam Berinsky, Vincent Hutchings, Tali Mendelberg, Lee Shaker, and Nicholas Valentino conducted experiments to examine people’s reactions to stimuli suggesting that either Barack Obama or, ironically enough, John Edwards were potentially guilty of “sexual indiscretion” (p.185; see p.198-200 for actual cues). Here’s their summary of the article and its findings:

A growing body of work suggests that exposure to subtle racial cues prompts white voters to penalize black candidates, and that the effects of these cues may inﬂuence outcomes indirectly via perceptions of candidate ideology. We test hypotheses related to these ideas using two experiments based on national samples. In one experiment, we manipulated the race of a candidate (Barack Obama vs. John Edwards) accused of sexual impropriety. We found that while both candidates suffered from the accusation, the scandal led respondents to view Obama as more liberal than Edwards, especially among resentful and engaged whites. Second, overall evaluations of Obama declined more sharply than for Edwards. In the other experiment, we manipulated the explicitness of the scandal, and found that implicit cues were more damaging for Obama than explicit ones. (emphasis added)